Vestigial: Adjective describing something that is a vestige (remnant) or a primitive structure, and no longer believed to be important. For example, the appendix is considered a vestigial organ, and some infants are born with a vestigial tail.
Vestigial Organs have never been defined as totally useless, despite creationist claims to the contrary. In fact, even Darwin recognized that vestigial organs can sometimes serve a small purpose. Yet I believe we do have many organs that are useless relics, reflecting our evolutionary history. Why do I think this? After all, just because I cannot think of a function for something does not mean it is totally useless. My answer: Let's look at natural selection: Natural Selection allows the "fittest" (best surving, most productive) creatures to become the most common in a population. No one has ever observed any different. Therefore, if a certain species' organ is useful, it will be present in almost every member of a species. Or at least, the individuals with that particular organ should be more "fit" and leave behind more offspring than those who don't, so that this organ (or trait) eventually becomes extremely common in a population. However, this is not the case with some of our organs, and several of these are extremely good evidence of our common ancestry with apes, mammals, reptiles, and so on. Even better, they are beginning to evolve away from the human species, indicating that they are indeed nonfunctional. For example:
NECK RIB
A set of cervical ribs—possibly leftovers from the age
of reptiles—still appear in less than 1 percent of the
population. They often cause nerve and artery
problems.
SUBCLAVIUS MUSCLE
This small muscle stretching under the shoulder from
the first rib to the collarbone would be useful if
humans still walked on all fours. Some people have
one, some have none, and a few have two.
PALMARIS MUSCLE
This long, narrow muscle runs from the elbow to the
wrist and is missing in 11 percent of modern humans.
It may once have been important for hanging and
climbing. Surgeons harvest it for reconstructive
surgery.
PLANTARIS MUSCLE
Often mistaken for a nerve by freshman medical
students, the muscle was useful to other primates for
grasping with their feet. It has disappeared
altogether in 9 percent of the population.
THIRTEENTH RIB
Our closest cousins, chimpanzees and gorillas, have an
extra set of ribs. Most of us have 12, but 8 percent
of adults have the extras.
BODY HAIR
Source: "Useless Body Parts" by Jocelyn Selim, Discover Magazine Vol. 25 No. 6
